The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC design and material have produced generations of ICs where each generation has smaller and more complex circuits than previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased.
This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of IC processing and manufacturing. For these advances to be realized, similar developments in IC processing and manufacturing are needed. Continuous advancements in lithographic resolution have been made to support critical dimensions (CDs) of 90 nm to 65 nm, 45 nm, 32 nm, 22 nm, 16 nm and beyond. New techniques in lithography have been developed, such as immersion lithography, multiple patterning, extreme ultraviolet (EUV) lithography and e-beam lithography. The challenges being raised by new lithography techniques are not only in resolution but also in economy (e.g. cost of upgrading and loss of throughput). Economy is often maintained by extending the use of existing lithography tools for advanced technology nodes. However, current methods have not been satisfactory in all respects.